The present invention relates to an automatic pipe welding apparatus and, more particularly, to an automatic pipe welding apparatus suitable for use in welding already-constructed pipings within a limited space.
Intricate arrangement of a large number of pipes of different diameters in nuclear power plants and chemical plants arouses a demand for a compact pipe welding apparatus, because the space available for installing new pipes and/or repairing already-constructed pipes is extremely limited.
For instance, assuming here a nuclear power plant in which pipes of 200 mm dia. are installed at a pitch of 150 mm, the diameterical thickness of the base member of the welding apparatus has to be as small as about 30 mm, when the height of the welding unit is taken into consideration.
Especially, in case of a repair of already-constructed pipes, the base member of the welding apparatus has to be divided into pieces, in order that it may clamp the pipe even in a limited space, without disassembling the pipes.
The specification of U.S. Pat. No. 3,277,567 discloses a pipe welding apparatus having a split type base member. However, this split type base member requires a large space, when it is fitted around the pipe, because two halves are moved apart from each other by a distance at least equal to the diameter of the pipe. Thus, the welding apparatus having a split type base member is not suitable for use in extremely limited space.
The demand for enhanced welding precision is also increasing. It is therefore strictly required that the welding torch is rotated concentrically with the pipe. To this end, it is necessary that the base member of the welding apparatus clamps the pipe exactly concentrically with the latter, and that the welding torch goes round the periphery of the pipe in a stable manner.
The specification of U.S. Pat. No. 3,389,846 discloses three clamping means for securing the base member to the pipe. However, a highly precise centering of the base member around the pipe cannot be performed by these clamping means, because these clamping means are operated independently from each other.
Also, the specification of U.S. Pat. No. 3,266,700 suggests the use of a plurality of clamping means. A cam ring is provided on the base member for interlocking these clamping means so that they may be operated simultaneously. However, the welding apparatus is rendered complicated and large-sized, because of the presence of a hydraulic cylinder for actuating the cam ring. In addition, since the base member of this type of welding apparatus cannot be divided into sections, the apparatus cannot be applied to the repair of pipes which are fixed at both ends.
Further, in case of the repair of pipes in nuclear plants, it is highly desirable that the welding can be correctly performed without necessitating the watch by operators, in order to avoid the accident attributable to the irradiation of radioactive rays. To this end, the welding apparatus has to automatically detect the portion of the pipe to be welded and automatically locate the welding torch correctly at the detected portion to be welded.